Synthesis of Anatase Nanopowders by Sol-gel Method and Influence of Temperatures of Calcination to Their Photocatalitic Properties

The titanium dioxide (TiO2) nanopowders were produced by sol-gel technique from tetrabutyl titanate as a precursor, varying the temperature of calcination (from 500 to 550 degrees C with the step of 10 degrees C). XRPD results have shown that all synthesized nanopowders are dominantly in anatase phase. The analysis of the shift and linewidth of the most intensive anatase E-g Raman mode confirmed the XRPD results and added the presence of small amount of highly disordered brookite phase in all samples. The analysis of pore structure from nitrogen sorption experimental data described all samples as mesoporous, with mean pore diameters in the range of 1.5 and 4.5 nm. Nanopowder properties have been related to the photocatalytic activity, tested in degradation of the textile dye (C.I. Reactive Orange 16). The sample calcined at temperature of 510 degrees C showed the best photocatalytic performance

Structural characterization of mechanically milled ZnO: influence of zirconia milling media

Zinc oxide nanoparticles were obtained by milling in a planetary ball mill with a zirconia milling assembly for up to 5 h in air. The samples were characterized by scanning electron microscopy, x-ray diffraction (XRD) and Raman spectroscopy methods. The deviation of the lattice parameters from single crystal values was related to defect creation and increase of strain inside the hexagonal lattice of milled ZnO nanoparticles. The observed redshift and peak broadening of the major first-order Raman modes were ascribed to the formation of intrinsic defects by mechanical milling combined with the effects of phonon confinement in nanosized powders. To investigate the type of intrinsic defects and impurities introduced during milling, it was necessary to analyze both milled and thermally treated ZnO. After thermal treatment, the intensity of the Raman spectra increased and the peak positions reverted to values similar to those in unmilled ZnO powder, pointing to defect annihilation. XRD patterns of sintered samples confirmed the existence of zirconia impurities and the Rietveld analysis revealed a small amount of zirconium introduced in the ZnO crystal lattice on the Zn sites or interstitial sites. The large influence of those impurities on the micro-Raman spectra of thermally treated samples was observed in this study

Far-infrared phonon spectroscopy of Cd1-xMnxS quantum dots

Phonon spectra of Cd1-xMnxS (x =0; 0.01; 0.05; 0.1; 0.15; 0.3) quantum dots (dsimilar to4.5 nm) are investigated by far-infrared reflection in the spectral range 80 - 600 cm(-1) and temperature range 80-300 K. The Cd1-xMnxS quantum dots have been synthesized by using aqueous solution precipitation. Together with the modes of (NaPO3)(6) surface active agent, and quantum dots CdS, we obtain a new mode of Mn at about 120 cm(-1). The position of this mode is discussed in the frame of the linear chain model with both mass and force constant defects.Progress in Advanced Materials and Processes, 5th Conference of the Yugoslav-Materials-Research-Society (Yu-MRS 2003), Sep 15-19, 2003, Herceg Novi, Yugoslavi

Photocatalytic degradation of alprazolam in water suspension of brookite type TiO2 nanopowders prepared using hydrothermal route

Two series of nanocrystalline brookite-type powders have been synthesized by using combined sal gel hydrothermal method with titanium tetrachloride (TiCI4) as a precursor and hydrothermal temperature and reaction time varied in the range of 120-200 degrees C and 12-48 h, respectively. The effects of chosen synthesis parameters on structural, morphological and optical properties of synthesized powders have been investigated by the XRPD, SEM, EDS and BET measurements, as well Raman spectroscopy and spectroscopic ellipsometry. The XRPD results have shown that pure brookite phase, with mean crystallite size of -33 nm, has been obtained only in the sample synthesized at 200 degrees C, after 24 h of hydrothermal process. In all other samples anatase phase also appears, whereas rutile and sodium titanate phases have been noticed in the samples synthesized at lower temperatures. The presence of different titania phases has also been confirmed and analyzed by Raman scattering measurements. The SEM measurements have shown spindle-like particles in brookite-rich samples synthesized at 200 degrees C, whereas BET measurements have detected mesoporous structure in these samples. The properties of synthesized powders have been correlated to their photocatalytic efficiency, tested in degradation of alprazolam, one of the 5th generation benzodiazepines. The sample consisted of pure brookite has shown the highest efficiency in the photodegradation of alprazolam, practically equal to the activity of Degussa P25

Cd1-xMnxS nanoparticles: Far-infrared phonon spectroscopy

Phonon spectra of Cd1-xMnxS (x = 0; 0.01; 0.05; 0.1; 0.15; 0.3) nanoparticles (d similar to 4.5 rim) have been investigated by far-infrared reflection (FIR) (spectral range 40 - 600 cm(-1), temperature range 80-300 K) and Raman spectroscopy (100 - 700 cm(-1), 300 K). Cd1-xMnxS nanoparticles have been synthesized by using aqueous solution precipitation. We obtained interesting features in FIR spectra: there are expected modes of bulk US (240 cm(-1), 300 cm(-1)), new modes connected with namo-size of US (130 cm(-1), 170 cm(-1)) and additional mode at 120 cm(-1) in Cd1-xMnxS nanoparticles which can be assigned to the presence of Mn. The position of obtained modes is discussed in the frame of the linear chain model with both mass and force constant defects. Raman spectroscopy gives us only the mode at 300 cm(-1) and its second harmonic.1st International Meeting on Applied Physics, Oct 13-18, 2003, Badajoz, Spai